APPLETON, Wis. (AP) — Republican presidential front-runner Mitt Romney on Friday defended his personal wealth amid intensifying criticism from his main GOP rival and President Barack Obama's re-election campaign, unlikely allies working to portray the former businessman as out of touch with most Americans.

Romney, who is worth up to $250 million, would be among the nation's richest presidents if elected. His Democratic and Republican opponents have thrust Romney's success to the forefront of the presidential contest as he tightens his grasp on the GOP nomination.

"If we become one of those societies that attacks success, one outcome is certain — there will be a lot less success," Romney said during a speech thick with general election undertones at Lawrence University in Appleton, Wis. "You're going to hear a deafening cacophony of charges and counter-charges and my prediction is that by Nov. 6 most of you are going to be afraid to turn on your TV."

The former Massachusetts governor argued his case several days before the GOP primary Tuesday in Wisconsin, a state that has general election implications as he courts the working-class voters who make up the bulk of the electorate.

Obama won Wisconsin by 14 percentage points in November 2008.

Speaking to Wisconsin voters 250 miles to the west, Rick Santorum suggested anew that Romney has little grasp of the problems facing working Americans.

"We need someone who can talk and relate to folks battling in this economy, not someone talking about being a CEO of a company and making jokes about firing people," Santorum said.

"No, I don't do very well among people with incomes over $200,000 in the Republican Party. Those aren't the Democrats and independents we're going to get in the general election," he said. "We're going to get the voters Ronald Reagan brought to the table — folks who are blue-collar folks who shared our values but were suspicious Republicans weren't on their side."

Though Romney grew up with wealth and privilege as the son of a Michigan governor, he has tried to downplay his early advantages and said in Friday's speech that he took "an entry-level job" after graduating from Harvard law and business schools.

"I loved cars and I was very tempted to stay in Michigan and go into the car business as he had, but I knew I would always wonder if any success I had was due to my father," Romney said. "So when I got out of business school, I stayed in Massachusetts where I went to school and got an entry-level job with the best company that would hire me."

Despite efforts to connect, Romney has repeatedly reminded voters — unintentionally — that he lives a different kind of life. He casually bet a rival $10,000 during a December presidential debate. He's adding several expensive upgrades, such as a car garage, to a home in California. And he's mentioned multiple times that his friends include the owners of professional sports teams.

Romney spent virtually his entire business career with Bain Consulting and Bain Capital, the Boston-based private equity firms where he earned the fortune that has allowed him to go for more than a decade without earning a regular paycheck.

Obama's campaign is pushing Romney to release years of tax returns dating to his career at the companies. The campaign distributed a Wall Street Journal article on Friday that raised questions about Romney's investment income.

"First, we learned that Gov. Romney may keep his investments offshore in order to claim special tax breaks," Obama spokesman Ben LaBolt said. "Now, we found out that he may have engaged in questionable maneuvers to drive up the value of his IRA."

Obama himself is far more wealthy than the average voter, though not in Romney's class, and he earned his fortune in recent years. The president and his wife, Michelle, reported income of $1.73 million in 2010, mostly from the books he's written, according to his tax return. That was down from the $5.5 million of a year earlier.

Rep. Paul Ryan, R-Wis., a rising star in the GOP who endorsed Romney on Friday, suggested that criticism from Obama and Santorum would fall flat.

"Here in Wisconsin we appreciate people who are successful. We reward hard work," Ryan said. "Since when is that a bad thing?"

Exit polling suggests that Romney may have to broaden his appeal to middle-class voters.

He has consistently performed better than his rivals among voters with higher family incomes. Although Romney has lost the overall vote in eight of the 18 states where exit or entrance polls were conducted, he only lost voters with six-figure incomes in three of them.

In Louisiana, the high-dollar tilt in Romney's support was particularly pronounced: A majority of those who voted for Romney had six-figure family incomes though that group made up just three in 10 voters.

He's trying to broaden his appeal, in part, by chatting about gambling.

"We were talking about that. I guess there is a massive, massive lottery," Romney said while visiting a restaurant Friday evening as Mega Millions ticketholders across the country awaited a record drawing. "I'm not planning on playing the lottery."

With a dry smile, he took a shot at a mega-donor and casino mogul who supports Newt Gingrich's campaign. "I understand that Sheldon Adelson has bought some tickets," he said.